An Automatic Transmission (AT), a Continuously Variable Transmission (CVT) or the like for an automobile is provided with a seal ring that seals the annular gap between a shaft and a housing that rotate relative to each other, to maintain hydraulic pressure. In recent years, an increase in fuel efficiency has been propelled as countermeasures for environmental issues, and there has been an increased demand for reducing a rotational torque in the above seal ring. In view of this, technology for providing a groove that guides sealed fluid to the side of the sliding surface of a seal ring to generate dynamic pressure has been known (see PTL 1). In such technology, however, when sealed fluid contains foreign matter, there is a possibility that the effect of reducing a rotational torque is not sufficiently exhibited with a reduction in dynamic pressure effect and that sealing performance reduces with the acceleration of wear-out as a result of the foreign matter being put in the groove.
In addition, there has been known technology for providing a groove, through which the side of an inner peripheral surface and the side of an outer peripheral surface communicate with each other, on the side of the sliding surface of a seal ring to remove foreign matter from the sliding surface of the seal ring (see PTL 2). In such technology, however, sealed fluid leaks from a groove. Therefore, there is a possibility that a leakage amount increases.